1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter referred simply as an LCD) and an image display device, and more particularly to the LCD used as a monitor or a like of a computer and provided with liquid crystal cells arranged in a matrix form and the image display device equipped with the above LCD.
The present application claims priority of Japanese Patent Application No. 2000-241714 filed on Aug. 9, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
FIG. 10 is a top view of an example of configurations of a conventional LCD constructed of a transverse electric field-type liquid crystal which has been disclosed in Japanese Laid-open Patent Application No. 2001-125122. Here, the transverse electric field-type liquid crystal refers to a liquid crystal in which an electric field is formed in a transverse direction (that is, in a direction parallel to an upper face on an glass substrate 1 being approximately quadrangular on which the LCD is formed) in a liquid crystal cell. The transverse electric field-type liquid crystal has a characteristic of having a small dependency on a viewing angle in contrast and therefore it is increasingly used in recent years.
The disclosed LCD is an active-matrix LCD using a TFT (Thin Film Transistor) as a switching element and, as shown in FIG. 11, includes a dot pixel portion 4 surrounded by a plurality of scanning lines 2 disposed at specified intervals in a column direction (that is, in a longitudinal direction) and a plurality of signal lines 3 disposed at specified intervals in a row direction (that is, in a transverse direction), a liquid crystal cell 5 mounted on each of the dot pixel portion 4 having a liquid crystal layer serving equivalently as a capacitive load, a pixel electrode 6 and a common electrode 8 formed opposite to each other in a manner that a liquid crystal layer is put between the pixel electrode 6 and the common electrode 8 and a TFT 7 whose source is connected to one end of the pixel electrode 6. The LCD in this example displays characters, images, or a like, while a common voltage Vcom is applied to the common electrode 8 through a common signal line 9 in each row and in each column, when a data signal produced based on a video signal is applied to the signal line 3 and when a scanning signal produced based on a horizontal sync signal and a vertical sync signal is applied to the scanning line 2. Each of the common signal lines 9 is connected to a common wiring 10 which is mounted in a shape of an approximate character xe2x80x9cxe2x80x9d (or the approximate character xe2x80x9cxe2x80x9d) (see FIG. 10) in a manner that it surrounds a display area 11 where the dot pixel portion 4 are arranged in a matrix form.
Moreover, though not shown in FIG. 11, more exactly, it can be considered as if an equivalent capacitors were to be formed by the liquid crystal layer serving as a dielectric in the liquid crystal cell 5 and by the pixel electrode 6 and the common electrode 8 sandwiching the liquid crystal layer in a manner to be opposite to each other and that other capacitors are further connected in parallel to the liquid crystal layer of the liquid crystal cell 5. These other capacitors are called a common storage in a sense that they are formed relative to the common electrode 8 and called an auxiliary capacitor in a sense that it helps the liquid crystal layer in the liquid crystal cell 5 to accumulate a signal charge for one vertical sync period of time.
In the LCD shown in FIG. 10, all the signal lines 3 are routed to an upper portion on an upper side of the display area 11 and divided into three blocks 121 to 123 and a plurality of signal lines 3 making up each of the blocks 121 to 123 is gathered in a manner to form an approximately trapezoidal shape and an end of each of the signal lines 3 is connected to each of corresponding signal terminals arranged at a predetermined pitch. Similarly, all the scanning lines 2 are routed both to a right portion on a right side of the display area 11 and to a left portion on a left side of the display area 11 and divided into three blocks 131 to 133 and 141 to 143 and a plurality of scanning lines 2 making up each of the blocks 131 to 133 and of the blocks 141 to 143 is gathered in a manner to form an approximately trapezoidal shape and an end of each of the scanning lines 2 is connected to each of corresponding scanning terminals arranged at a predetermined pitch. A pair of the scanning terminals disposed in a position symmetrical right and left is connected to each other through the same scanning line 2.
The common wiring 10, as shown in FIG. 10, is mounted in a portion adjacent to the display area 11 in a shape of the approximate character xe2x80x9cxe2x80x9d (or the approximate character xe2x80x9cxe2x80x9d). The common wiring 10 is routed to an upper portion of the glass substrate 1 along both ends of each of the blocks 121 to 123 in the upper portion on the upper side of the display area 11 to form routing sections 10a1 to 10a6. The common wiring 10 is routed to a leftmost portion of the glass substrate 1 along both ends of each of the blocks 131 to 133 in the left portion on the left side of the display area 11 to form the routing sections 10b1 to 10b6. The common wiring 10 is routed to a rightmost portion of the glass substrate 1 along both ends of each of the blocks 141 to 143 in the right portion on the right side of the display area 11 to form the routing sections 10c1 to 10c6. An end of each of the routing sections 10a1 to 10a6, 10b1 to 10b6, and 10c1 to 10c6 is connected to each of corresponding common terminals 151 to 156, 161 to 166, and 171 to 176 respectively.
The aim of dividing the scanning lines 2 and signal lines 3 into blocks 121 to 123, 131 to 133, and 141 to 143 each having specified numbers of lines and of forming each of the routing sections 10a1 to 10a6, 10b1 to 10b6, and 10c1 to 10c6 of the common wiring 10 along both ends of corresponding blocks 121 to 123, 131 to 133, and 141 to 143 and of routing the scanning lines 2 and signal lines 3 to form the approximately trapezoidal shape so that each of the end portions is connected to each of the scanning terminal and of the signal terminals and each of common terminals being mounted to be placed at the specified pitch, is to place each of terminals and end portions fixedly in a specified position. Also, the aim of placing each of terminals and end portions fixedly in the specified position is to enable a package being one of a TCP (Tape Carrier Package) mounted by using TAB (Tape Automated Bonding) technology and being used in a driving circuit to drive the LCD to be commonly used in different kinds of the LCDS. The LCD, while the TCP is connected, by using a thermo compression bonding method, to the scanning terminals and signal terminals connected to the blocked scanning lines 2 and signal lines 3 and common terminals 151 to 156, 161 to 166, and 171 to 176 connected to the common wiring 10, is connected to a driving circuit mounted on the TCP or a printed board through the TCP. That is, by arranging each of the terminals and end portions at the specified pitch being common to various types of the LCD, each of terminals of the TCP to be connected to these terminals can be placed in a specified position accordingly and a package for the driving circuit being the TCP can be used commonly in different kinds of the LCDs.
By configuring above, since common terminals 151 to 156, 161 to 166, and 171 to 176 for every block made up of the scanning lines 2 and signal lines 3 are provided, wiring resistance of the common wiring 10 can be dispersed more and can be reduced more, as a whole, compared with a case in which the common terminal are mounted simply on both ends in the upper portion on the upper side, in the right portion on the right side and in the left portion on the left side of the display area 11 (that is, a case in which, in FIG. 10, only the common terminals 151, 156, 161, 166, 171, and 176 were to be provided), as a result, crosstalk and/or dispersion in luminance among the dot pixel portions 4 can be reduced.
However, when the above conventional LCD is used as a monitor for a computer or a like, it presents the following problems.
Let it be assumed that an image as shown in FIG. 12 is displayed on a color LCD called an SXGA (Super Extended Graphics Array) which can provide a resolution of 1280 pixelsxc3x971024 pixels. In this color LCD, color filters are arranged in a stripe manner in which color filters for three primary colors R (red), G (green), and B (blue) each corresponding to each of the liquid crystal cell 5 are arranged repeatedly in order of R, G, and B colors each corresponding to each of the liquid crystal cell 5 in a row direction and color filters for the same colors are arranged repeatedly in a column direction, and one pixel is made up of three dot pixel portions 4 for the R, G, and B colors. Therefore, the number of dot pixel portions 4 of the LCD of the example is 3840 xc3x971024 pixels. Hereinafter, a shape of an image to be displayed is expressed by the number of the dot pixel portions 4. In FIG. 12, a central window portion is of a quadrangular shape made up of 3072xc3x97256 pixels by which a white color is displayed, and the background portion surrounding the above window portion has a width of 384 pixels and formed in a shape of the character xe2x80x9cxe2x80x9d, which displays a stripe in which a white and a black color alternately and repeatedly appear for each pixel made up of three dot pixels portions 4 for the R, G, and B colors. Moreover, to drive the above color LCD, a dot reverse driving method is employed in which a data signal whose voltage to be applied to the pixel electrode 6 is reversed for every dot pixel portion 4 relative to a common voltage Vcom being applied to the common electrode 8, is fed to the signal line 3. The dot reverse driving method is conventionally used widely for driving the color LCD because a life of the color LCD is shortened if the voltage of a same polarity continues to be applied to its liquid crystal cell 5 and because, even if the voltage to be applied to the liquid crystal cell 5 becomes opposite in polarity, the liquid crystal 5 can maintain all the same transmitted light characteristic. Moreover, in this color LCD, a so-called normally black mode in which, in a state of no voltage applied, transmittance of light through the liquid crystal is low, is employed and, when an absolute value of a voltage to be applied to the liquid crystal layers in the three dot pixels portions 4 for R, G, and B colors making up one pixel is approximately 0 volts, a black color is displayed while an absolute value of the voltage to be applied to the liquid crystal layers in the three dot pixels portions 4 for the R, G, and B colors making up one pixel is approximately 5 volts, a white color is displayed.
First, to the liquid crystal layer in each of dot pixel portions 4 connected to the scanning lines 2 which transverses across a background portion shown in FIG. 12 is applied a data signal having a voltage shown in FIG. 13A. That is, to the liquid crystal layer in the dot pixel portions 4 for the R and B colors, out of the three dot pixels portions 4 for the R, G, and B colors making up one pixel to display a white color, is applied a voltage having an absolute value of Vp (in the example, 5 V) which is of positive polarity relative to the common voltage Vcom and to the liquid crystal layer in the dot pixel portion 4 for the G color is applied a voltage having an absolute value of Vp (in the example, 5 V) which is of negative polarity relative to the common voltage Vcom. On the other hand, to the liquid crystal layer in the dot pixel portions 4 for the R and B colors, out of the three dot pixels portions 4 for the R, G, and B colors making up one pixel to display a black color, is applied a voltage having an absolute value of approximately 0 V which is of positive polarity relative to the common voltage Vcom and to the liquid crystal layer in the dot pixel portion 4 for the G color is applied a voltage having an absolute value of approximately 0 V which is of negative polarity relative to the common voltage Vcom. When the data signal having voltages shown in FIG. 13A is fed through the signal line 3 to the liquid crystal layer in each of the dot pixel portions 4, the common voltage Vcom is changed by a coupling capacitor existing between each of the signal lines 3 and each of the common signal line 9 to which the common voltage Vcom is applied. Though the number of dot pixel portions 4 connected to one scanning line 2 is made up of 3840 pixels, since the stripe in which the white color and the black color appears repeatedly for one pixel in the background portion and the voltage having an absolute value of 0 V is applied to a half (1920 pixels) of the pixels of the dot pixel portion 4 displaying the black color, the applied voltage hardly contributes to the change in the common voltage Vcom. Moreover, out of the three dot pixels 4 portions 4 for the R, G, and B colors making up one pixel, though a polarity of the liquid crystal layers in the dot pixel portion for the R color and the liquid crystal layer in the dot pixel portion 4 for the G color being adjacent to each other is different, since the voltage having the same absolute value Vp (in the example, 5 V) is applied, the change in the common voltage Vcom is cancelled out. That is, out of the dot pixel portion 4 made up of 3840 pixels, the dot pixel portion 4 contributing to the change in the common voltage Vcom is the dot pixel portion 4 for the B color making up the pixel displaying the white color and the number of pixels making up the dot pixel portion 4 is 640 pixels as obtained by an equation (1).
3840/(2xc3x973)=640xe2x80x83xe2x80x83(1) 
Thus, due to an influence of the voltage having an absolute value 5 V applied to the liquid crystal layer of 640 pixels out of the 3840 pixels, the common voltage Vcom is changed to be a common voltage Vxe2x80x2 com as shown in FIG. 13 (1). Because of this, since same results occur as if a voltage having an absolute value Vp1 being smaller than the absolute value of Vp were to be applied to the liquid crystal layer in the dot pixel portions 4 for the R and B colors and as if a voltage having an absolute value Vp2 being larger than the absolute value of Vp were to be applied to the liquid crystal layer in the dot pixel portion 4 for the G color, a stripe in greenish color, as a whole, instead of the stripe in the white and black colors originally expected, is displayed in the background portion. Moreover, when the color filters for three colors are arranged in order of the G, R, and B colors, a stripe in reddish color as a whole is displayed. When the color filters for three colors are arranged in order of the R, B, and G colors, a stripe in bluish color as a whole is displayed. Such the phenomenon is hereinafter called color degradation.
On the other hand, to the liquid crystal layer in each of the dot pixel portion 4 connected to the scanning line 2 which transverses across the window shown in FIG. 12 is applied a data signal having voltages shown in FIG. 13B. That is, in the background portion and the window portion, to the liquid crystal layer in the dot pixel portions 4 for the R and B colors, out of the three dot pixels portions 4 for the R, G, and B colors making up one pixel displaying a white color, is applied a voltage having an absolute value of Vp (in the example, 5 V) which is of positive polarity relative to the common voltage Vcom and to the liquid crystal layer in the dot pixel portion 4 for the G color is applied a voltage having an absolute value of Vp (in the example, 5 V) which is of negative polarity relative to the common voltage Vcom. On the other hand, to the liquid crystal layer in the dot pixel portions 4 for the R and B colors, out of the three dot pixels portions 4 for the R, G, and B colors making up one pixel to display the black color, is applied a voltage having an absolute value of approximate 0 V which is of positive polarity relative to the common voltage Vcom and to the liquid crystal layer in the dot pixel portion 4 for the G color is applied a voltage having an absolute value of approximate 0 V which is of negative polarity relative to the common voltage Vcom. In this case, when the data signal having voltages shown in FIG. 13A is applied through the signal line 2 to the liquid crystal layer in each of the dot pixel portion 4 connected to the same scanning line 2, though, due to the coupling capacitor existing between each of the signal lines 3 and the common signal line 9 to which the common voltage Vcom is applied, the common voltage Vcom is changed, an amount of the change is smaller when compared with the case shown in FIG. 13A. That is, in the dot pixel portion 4 made up of 3072 pixels forming the window portion, out of the dot pixel portion 4 made up of 3840 pixels, since a voltage having an absolute voltage of Vp (in the example, 5 V) is applied to the liquid crystal layers in all dot pixel portions 4, the change in the common voltage Vcom between the dot pixel portions 4 being adjacent to each other is cancelled out. In the dot pixel portion 4 made up of 768 pixels (3840 pixelsxe2x88x923072 pixels) forming the background portion, since the same as in the case shown in FIG. 13A can be applied thereto, the dot pixel portion 4, out of the dot pixel portion 4 made up of 3840 pixels, contributing to the change in the common voltage Vcom is the dot pixel portion 4 for the B color making up the pixel to display the white color in the dot pixel portion 4 made up of 768 pixels forming the background portion, the number of the pixels of which is 128 pixels as obtained by an equation (2).
(3840xe2x88x923071)/(2xc3x973)=128xe2x80x83xe2x80x83(2) 
Thus, due to an influence by the voltage having the absolute value of 5 V applied to the liquid crystal layer in the dot pixel portion 4 made up of 128 pixels, out of the dot pixel portion 4 made up of 3840 pixels, the common voltage Vcom is changed to the common voltage Vxe2x80x2 com as shown in FIG. 13B, however, the change is smaller when compared with the case shown in FIG. 13A. Therefore, the color degradation described above is reduced. A phenomenon that a difference is produced in the color degradation between the dot pixel portion 4 connected to the scanning line 2 traversing across the background portion and the dot pixel portion 4 connected to the scanning line 2 traversing across the window portion is hereinafter called horizontal stroke. Such the phenomena as the color degradation or horizontal stroke occur because wiring resistance at each of the routing sections 10a1 to 10a6, 10b1 to 10b6, and 10c1 to 10c6 is comparatively large, which causes the common voltage Vcom to be applied to these routing sections to be readily changed.
There is a possibility that such the phenomena as the color degradation and horizontal stroke occur, more or less, even in a TN (Twisted Nematic)xe2x80x94LCD whose dot pixel portion 4 has configurations as shown in FIG. 14 and a common storage (in FIG. 14, same reference numbers are assigned to parts having the same function as those in FIG. 11 and their descriptions are omitted accordingly). The reason is that, if configurations of the routing sections 10a1 to 10a6, 10b1 to 10b6 and 10c1 to 10c6 are approximately the same as those shown in FIG. 19, the resistance at the routing section affects the change in the common voltage more or less. Moreover, in FIG. 14, the common signal line 9 serves also as the common electrode 8.
Since each of the routing sections 10a1 to 10a6, 10b1 to 10b6 and 10c1 to 10c6 of the common wiring 10 is formed along both ends of the blocks 121 to 123, 131 to 133, and 141 to 143, light from a backlight leaks from a clearance between blocks being adjacent to each other, causing irregularity of luminance at edge portions surrounding the display area 11. This phenomenon is hereinafter called luminance irregularity.
In view of the above, it is an object of the present invention to provide an LCD capable of reducing wiring resistance at routing sections of common wirings and changes in a common potential to be applied to the common wiring to decrease xe2x80x9ccolor degradationxe2x80x9d and xe2x80x9chorizontal strokexe2x80x9d and xe2x80x9cluminance irregularityxe2x80x9d and an image display device equipped with the above LCD.
According to a first aspect of the present invention, there is provided a liquid crystal display including:
a liquid crystal cell disposed at each point of intersections of a plurality of scanning lines, extending in a row direction, mounted at specified intervals in a display area being approximately quadrangular in shape placed at a predetermined position on a glass substrate being approximately quadrangular in shape and of a plurality of signal lines, extending in a column direction, mounted at specified intervals and containing a common electrode;
signal terminals mounted at either or both of upper end portions or lower end portions of the glass substrate at a specified pitch, to which end portions of the signal lines routed to either or both of an upper portion on an upper side or of a lower portion on a lower side of the display area and divided into two or more blocks and gathered are connected;
scanning terminals mounted at either or both of left end portions or right end portions of the glass substrate at a specified pitch, to which end portions of the scanning lines routed to either or both of a left portion on a left side or of a right portion on a right side of the display area and divided into two or more blocks and gathered are connected;
common signal lines each being mounted in each row and each column in the display area used to apply a common voltage to the common electrode;
common wirings each being mounted at either or both of an upper portion on an upper side or of a lower portion on a lower side of the display area and mounted at either or both of a left portion on a left side or of a right portion on a right side of the display area, to which each of end portions of a plurality of the common signal lines is connected;
a first routing section made up of a metal film having very low transmittance of light emitted from a backlight and formed in a manner that a gap between blocks being adjacent to each other along one side of the display area is almost filled in, and wherein one portion facing the display area of which is connected to the common wiring;
a second routing section made up of the metal film and formed in a manner that a region surrounded by an outer side portion of each of the blocks and by straight lines being four side lines of the display area being extended toward an end portion of the glass substrate is almost filled in, and wherein the one portion facing the display area of which is connected to the common wiring; and
a plurality of common terminals mounted so as to be adjacent to the signal terminal or the scanning terminal connected to an end portion of each of the signal lines or the scanning lines making up an outermost portion of each of the blocks and formed on the first routing section and the second routing section at an end portion of the glass substrate.
In the foregoing, a preferable mode is one wherein the first routing section and the second routing section formed at either or both of the left portion on the left side or of the right portion on the right side of the display area are formed on a same layer as a plurality of the scanning lines is formed and connected to the common wiring through a contact hole and wherein the first section and the second section formed at either or both of the upper portion on the upper side or of the lower portion on the lower side of the display area are formed on a same layer as a plurality of the signal lines is formed and connected to the common wiring through the contact hole.
According to a second aspect of the present invention, there is provided a liquid crystal display including:
a liquid crystal cell disposed at each point of intersections of a plurality of scanning lines, extending in a row direction, mounted at specified intervals in a display area being approximately quadrangular in shape placed at a predetermined position on a glass substrate being approximately quadrangular in shape and of a plurality of signal lines, extending in a column direction, mounted at specified interval, and containing a common electrode;
signal terminals mounted at either or both of upper end portions or lower end portions of the glass substrate at a specified pitch, to which end portions of the signal lines routed to either or both of an upper portion on an upper side or of a lower portion on a lower side of the display area and divided into two or more blocks and gathered are connected;
scanning terminals mounted at either or both of left end portions or right end portions of the glass substrate at a specified pitch, to which ends of the scanning lines routed to either or both of a left portion on a left side or of a right portion on a right side of the display area and divided into two or more blocks and gathered are connected;
common signal lines each being mounted in each row and each column in the display area used to apply a common voltage to the common electrode;
common wirings each being mounted at either or both of an upper portion on an upper side or of a lower portion on a lower side of the display area and mounted at either or both of a left portion on a left side or of a right portion on a right side of the display, to which each of end portions of a plurality of the common signal lines is connected;
a first routing section made up of a metal film having very low transmittance of light emitted from a backlight and formed in a manner that a gap between blocks, being adjacent to each other, formed in a manner so as to surround the display area, is almost filled in, and wherein one portion facing the display area of which is connected to the common wiring;
a second routing section made up of the metal film and formed in a manner that a region surrounded by an outer side portion of each of the blocks and by a straight line being one side being orthogonal to one side of the display area along which the block contacts, being extended toward an end portion of the glass substrate, is almost filled in, and wherein one portion facing the display area of which is connected to the common wiring; and
a plurality of common terminals mounted so as to be adjacent to the signal terminal or the scanning terminal connected to an end portion of the signal line or the scanning line making up an outermost portion of each of the blocks and formed on the first and second routing sections at an end portion of the glass substrate.
In the foregoing, a preferable mode is one wherein the first routing section facing a corner portion of the display area is made up of a first approximate trapezoidal portion formed on a same layer as a plurality of the scanning lines is formed and of a second approximate trapezoidal portion formed on a same layer as a plurality of the signal lines is formed,
wherein the first approximate trapezoidal portion is formed in a manner that it reaches a place being positioned opposite to the scanning line disposed at an outermost portion of the adjacent blocks where a straight line connecting an end of each of the signal terminals mounted at the specified pitch and an end of each of the scanning terminals on a side of the display area is extended and where the common wiring is extended,
wherein the second approximate trapezoidal portion is formed in a manner that it reaches a place being positioned opposite to the signal line disposed at an outermost portion of the adjacent blocks where a straight line connecting an end of each of the signal terminals mounted at the specified pitch and an end of each of the scanning terminals on a side of the display area is extended and where the common wiring is extended, and
wherein the first approximate trapezoidal portion and the second approximate trapezoidal portion are connected to each other at a portion where they are overlapped through contact holes with specified numbers and at a specified pitch.
Also, a preferable mode is one wherein each of the common wirings is made up of a longitudinal line and a horizontal line contacting sides of the display area and wherein the longitudinal line is formed on a same layer as a plurality of the signal lines is formed and the horizontal line is formed on a same layer as a plurality of the scanning lines is formed and the common wirings are connected to each other at a region where the longitudinal line and horizontal line are overlapped through contact holes and wherein each of the common signal lines is formed on a same layer as each of a plurality of the scanning lines is formed and connected to the longitudinal line through contact holes.
Furthermore, a preferable mode is one wherein the first routing section the and second routing section are formed in a manner that each of the routing sections is placed far, by an interval being equal to a predetermined pitch, from the scanning lines or the signal lines being positioned at outermost portions of blocks adjacent to each other.
According to a third aspect of the present invention, there is provided an image display device including a liquid crystal display stated above.
With the above configurations, there are provided a first routing section made up of a metal film having very low transmittance of light emitted from a backlight and formed in a manner that a gap between blocks being adjacent along one side of a display area is almost filled in and a second routing section made up of the above metal film and formed in a manner that a region surrounded by an outer side portion of a block mounted outside the display area and by straight lines being four sides of the display area which have extended toward end portions of a glass substrate are almost filled in and, therefore, wiring resistance at a routing section of common wirings can be reduced and changes in common potential to be applied to the common wirings can be reduced, which enables xe2x80x9ccolor degradationxe2x80x9d and xe2x80x9chorizontal strokexe2x80x9d to be decreased in the LCD. Also, by using the metal film having very low transmittance of light, xe2x80x9cluminance irregularityxe2x80x9d can be also reduced.